Constant voltage circuit and infrared remote control receiver using the same

Abstract

A direct current input power supply voltage Vcc is outputted to the load side via a PNP type transistor having a small Vce. A base thereof is driven by a base current from which noise is removed in a power source noise removing circuit. An input to the noise removing circuit is produced by shifting a level from the Vcc side by a direct current level shift circuit. Since an output voltage Vs varies with reference to Vcc and a voltage drop is relatively small owing to the transistor, an operation voltage on the load side can be ensured. The noise removing circuit is constituted by a gm amplifier. In order to increase a noise removing rate at low frequencies, by setting gm of a time constant C/gm to a small value, it is possible to set a capacity to a value which allows integration.

What is claimed is:  
     
       1. A constant voltage circuit which removes power source noise by outputting a direct current constant voltage responsive to a direct current input power supply voltage, 
       the constant voltage circuit comprising:  
       a direct current level shift circuit for effecting a shift from the input power supply voltage by a predetermined direct current voltage level;  
       a power source noise removing circuit including a transconductance amplifier, for removing the power source noise from an output of the direct current level shift circuit; and  
       a PNP type transistor interposed in series with a power supply line between input and output terminals, a base of the PNP type transistor being driven by an output from the power source noise removing circuit.  
     
     
       2. The constant voltage circuit of  claim 1 , 
       wherein a level shift amount in the direct current level shift circuit is set to around a collector-emitter saturation voltage of the PNP type transistor.  
     
     
       3. The constant voltage circuit of  claim 1 , wherein an input circuit of the transconductance amplifier constituting the power source noise removing circuit is provided with first to fourth transistors of a same conducting type and a resistor; 
       bases or gates of the first and second transistors are connected to each other to become a first input terminal of the transconductance amplifier, and emitters or sources of the first and second transistors are connected to a first constant current source in common;  
       bases or gates of the third and fourth transistors are connected to each other to become a second input terminal of the transconductance amplifier, and emitters or sources of the third and fourth transistors are connected to a second constant current source in common;  
       the emitters or sources of the first and second transistors are connected to the emitters or sources of the third and fourth transistors via the resistor; and  
       collectors or drains of the first and fourth transistors are connected to a power source terminal.  
     
     
       4. The constant voltage circuit of  claim 1 , wherein 
       an output circuit of the transconductance amplifier constituting the power source noise removing circuit is provided with fifth and sixth transistors of different conducting types from each other;  
       a base or gate of the fifth transistor is connected to a base or gate of the sixth transistor; and  
       a capacity of the transconductance amplifier is charged and discharged by a base or gate current.  
     
     
       5. The constant voltage circuit of  claim 4 , wherein 
       the output circuit of the transconductance amplifier constituting the power source noise removing circuit is further provided with, in correspondence with the fifth and sixth transistors, seventh and eighth transistors of different conducting types from each other;  
       the fifth transistor of one conducting type is paired with the sixth transistor of the other conducting type, and the seventh transistor of one conducting type is paired with the eighth transistor of another conducting type;  
       a base or gate of the seventh transistor is connected to a base or gate of the eighth transistor, collectors or drains of the fifth and seventh transistors are connected to a ground (GND) or a power source in common, a collector or drain of the sixth transistor is connected to the power source or the GND, an emitter or source of the sixth transistor is connected to a collector or drain of the eighth transistor, and an emitter or source of the eighth transistor is connected to the GND or the power source; and  
       a differential current is inputted from the input circuit to emitters or sources of the fifth and seventh transistors.  
     
     
       6. The constant voltage circuit of  claim 5 , wherein 
       of the fifth to eighth transistors, transistors which use a minute base or gate current are PNP type transistors, which transistors are formed so as to be of a lateral structure, and with respect to the PNP type transistors, a parasitic photocurrent compensating circuit is disposed.  
     
     
       7. The constant voltage circuit of  claim 5 , wherein 
       of the fifth to eighth transistors, transistors which use a minute base or gate current are PNP type transistors, which PNP type transistors are formed so as to be of a vertical structure.  
     
     
       8. The constant voltage circuit of  claim 5 , wherein 
       a voltage is supplied to the collector of at least one of the fifth and seventh transistors, and collector-emitter voltages of the transistors are set to a substantially equal value.  
     
     
       9. The constant voltage circuit of  claim 5 , wherein 
       an input of a first buffer circuit is connected to the base or gate of at least one of the fifth and seventh transistor, and an output of the buffer circuit is connected to the collector or drain of the aforementioned transistor.  
     
     
       10. The constant voltage circuit of  claim 5 , wherein 
       an input of a first buffer circuit is connected to the base or gate of at least one of the fifth and seventh transistors, a level adjusting circuit which shifts a direct current level is added to an output of the first buffer circuit, an input of a second buffer circuit is connected to an output of the level adjusting circuit, and an output of the second buffer circuit is connected to the collector or drain of at least one of the fifth and seventh transistors.  
     
     
       11. An infrared remote control receiver comprising the constant voltage circuit of  claim 1 .